Steady-state isotopic transient kinetic analysis on Pd-supported hexaaluminates used for methane combustion in the presence and absence of NO

Autor: Meltem Ocal, Rachid Oukaci, Geroge Marcelin, Ben W-L Jang, James J. Spivey
Rok vydání: 2000
Předmět:
Zdroj: Catalysis Today. 59:205-217
ISSN: 0920-5861
DOI: 10.1016/s0920-5861(00)00284-4
Popis: This paper presents a study for the combustion of methane in the presence and absence of NO over hexaaluminates (La 1− X Sr X MnAl 11 O 19 ) and Pd-supported hexaaluminates (Pd/La 1− X Sr X MnAl 11 O 19 ). All the catalysts were subjected to a reaction cycle comprising of (1) CH 4 +O 2 , (2) CH 4 +O 2 +NO, and (3) CH 4 +O 2 reactions at temperatures between 300 and 700°C. Steady-state isotopic transient kinetic analysis (SSITKA) technique was employed to determine the surface lifetimes ( τ ), average site activities ( k ), and surface concentrations ( N ) of each relevant species during the reactions (1) and (2), as described above, on La 0.6 Sr 0.4 MnAl 11 O 19 and 0.9% Pd/La 0.6 Sr 0.4 MnAl 11 O 19 . The SSITKA experiments were performed at temperatures of 360–440°C. Steady-state results showed that the contribution of homogeneous gas phase reactions are appreciable in the presence of NO at temperatures above 650°C. Steady-state and SSITKA reactions on La 0.6 Sr 0.4 MnAl 11 O 19 suggested that methane and NO oxidation occur on the catalyst surface at 440°C. Steady-state and SSITKA reactions on Pd/La 0.6 Sr 0.4 MnAl 11 O 19 showed that the presence of NO 2 (formed via NO and O 2 ) boosted the site activity required for the formation of CO 2 . In the reaction where NO is involved, NO acts indirectly as chain initiator in the form of NO 2 , and also as chain terminator.
Databáze: OpenAIRE
Externí odkaz: